improve gdal_translate()

[gok@…]

To make gdal_translate() "smarter" add code below (started from line 621).
It will allow to use area of interest (AOI) window not exactly inside image area. Now AOI will be clipped to image border and will continue operation.

621: anSrcWin[0] = (int) 
            ((dfULX - adfGeoTransform[0]) / adfGeoTransform[1] + 0.001);
        anSrcWin[1] = (int) 
            ((dfULY - adfGeoTransform[3]) / adfGeoTransform[5] + 0.001);
		
        anSrcWin[2] = (int) ((dfLRX - dfULX) / adfGeoTransform[1] + 0.5);
        anSrcWin[3] = (int) ((dfLRY - dfULY) / adfGeoTransform[5] + 0.5);
		
        if( !bQuiet )
            sprintf( errMsg, 
			"Computed -srcwin %d %d %d %d from projected window.\n",
			anSrcWin[0], 
			anSrcWin[1], 
			anSrcWin[2], 
			anSrcWin[3] );

//todo: make it smarter:		
		if ( anSrcWin[0] < 0 ) {anSrcWin[2] += anSrcWin[0]; anSrcWin[0] = 0;}
		if ( anSrcWin[1] < 0 ) {anSrcWin[3] += anSrcWin[1]; anSrcWin[1] = 0;}
		if ( (anSrcWin[0] + anSrcWin[2]) > nRasterXSize ) {anSrcWin[2] = nRasterXSize - anSrcWin[0];}
		if ( (anSrcWin[1] + anSrcWin[3]) > nRasterYSize ) {anSrcWin[3] = nRasterYSize - anSrcWin[1];}
        
        if( anSrcWin[0] < 0 || anSrcWin[1] < 0 
            || anSrcWin[0] + anSrcWin[2] > nRasterXSize 
            || anSrcWin[1] + anSrcWin[3] > nRasterYSize )
        {

[warmerdam]

Gok,

I am concerned that adjusting the window is dangerous and people may not 
realize what is happening.  I would prefer to take the approach of 
allowing specification of a larger than original window by appropriate setup of 
a larger than original virtual file.  But that will require more complex
changes to the code. 

Thanks for the proposed patch anyways, and I imagine it will work well for
your needs.